/*
 * ==========================================================================*\
 * | $Id$
 * |*-------------------------------------------------------------------------*|
 * | Copyright (C) 2009 Virginia Tech | | This file is part of CloudSpace. | |
 * CloudSpace is free software; you can redistribute it and/or modify | it under
 * the terms of the GNU General Public License as published | by the Free
 * Software Foundation; either version 3 of the License, or | (at your option)
 * any later version. | | CloudSpace is distributed in the hope that it will be
 * useful, | but WITHOUT ANY WARRANTY; without even the implied warranty of |
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | GNU General
 * Public License for more details. | | You should have received a copy of the
 * GNU General Public License | along with CloudSpace; if not, see
 * <http://www.gnu.org/licenses/>.
 * \*==========================================================================
 */

package cloudspace.security.permissions;

import cloudspace.security.CloudSpaceUser;


// -------------------------------------------------------------------------
/**
 * Represents a directory permission token that always denies access. This is a
 * singleton fallback token that is used when no valid permissions are found for
 * a particular user and resource.
 * 
 * @author Tony Allevato
 * @author Last changed by $Author$
 * @version $Revision$, $Date$
 */
public class NoAccessPermissionToken extends PermissionToken
{
    // ~ Constructors ..........................................................

    // ----------------------------------------------------------
    /**
     * Initializes a new instance of the NoAccessPermissionToken class.
     */
    private NoAccessPermissionToken()
    {
        super( false, false );
    }


    // ~ Methods ...............................................................

    // ----------------------------------------------------------
    /**
     * Gets the single instance of the NoAccessPermissionToken class.
     * 
     * @return the single instance of the token
     */
    public static NoAccessPermissionToken getInstance()
    {
        if ( instance == null )
        {
            instance = new NoAccessPermissionToken();
        }

        return instance;
    }


    // ----------------------------------------------------------
    @Override
    public int getSpecificity()
    {
        // Not actually used.
        return 0;
    }


    // ----------------------------------------------------------
    @Override
    public boolean matchesUser( CloudSpaceUser user )
    {
        // Not actually used.
        return true;
    }


    // ----------------------------------------------------------
    @Override
    public boolean isSimilarTo( PermissionToken token )
    {
        return ( token instanceof NoAccessPermissionToken );
    }

    // ~ Static/instance variables .............................................

    private static NoAccessPermissionToken instance;
}
